I see. But in branch v1.8, in 31869, Ralph reverted the commit which moved del_procs after the barrier:
"Revert r31851 until we can resolve how to close these leaks without causing the usnic BTL to fail during disconnect of intercommunicators
Refs #4643"
Also, we need an rte barrier after del_procs - because otherwise rankA could call pml_finalize() before rankB finishes disconnecting from rankA.

I think the order in finalize should be like this:
1. mpi_barrier(world)
2. del_procs()
3. rte_barrier()
4. pml_finalize()